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Missing the point; Edison vs Tesla; AC vs DC power

DC for data centers at Gigaom has some good history and a few interesting tidbits on a trend towards DC in data centers. They miss the big issue, though.

The reason that Tesla and Westinghouse won out over Edison in establishing AC as the power distribution standard was about electrical power delivery over distance. With AC, transformers made it easy to step voltage up for transmission lines. That reduced current needed for a given power level and that reduced current reduced losses. There were other advantages, especially back in the day, as equipment power supplies and motors could also be made more efficient with AC (remember vibrating power supplies for car radios back when 6v and tube radios were the thing?) (See wikipedia on power transmission)

As Kanellos notes at Gigaom, DC is gaining some popularity. Part of this is the ‘alternative’ energy systems that depend upon batteries, part is the local distribution of power, and part is technology advances that make conversion between AC and DC less expensive and more efficient. These advances have also made power transmission of DC more economically feasible in some cases (see the Wikipedia article)

To solve the mismatch, a whole industry of AC-DC converters has been developed. National Semiconductor sells billions of dollars of worth of chips to convert power. Inverters in the solar industry exist to converts DC from solar panels to AC that can run on the wires in your home.

The data centers tend to use medium voltage DC – 48 volts. Low voltage – 12 VDC – can be found for most of the wall warts you find with external disk drives, small TV’s, and other such equipment.

AC power transmission has a lot of interesting engineering when in a grid. Keeping the phase in synchronization between all parts of the system can be a challenge. Impedance matching with loads can be a challenge. Noise, like lightning, can be a problem. The fact that we depend upon electrical power as a matter of course and rarely even notice its presence says a lot about an amazing engineering feat.

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